PSY2061 Chapter 11: PSY2061 – Readings – Week 8 – Learning
5 Jun 2018
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PSY2061 – Readings – Week 8 – Learning, memory and amnesia
• learning and memory - both neuroplastic processes - deal with the ability
of the brain to change its functioning on response to experience
• learning - deal with how experience changes the brain
• memory - deals with how these changes are stored and subsequently
reactivated
• amnesia - any pathological loss of memory
• amnesic effects of bilateral medial temporal lobectomy
•
o HM
o
▪ medial portions of his temporal lobes removed for the
treatment of epilepsy
▪ had a total inability to form new long-term memories
▪ formal assessment of HM’s anterograde amnesia - discovery
of unconscious memories
▪
▪ five tests were used to assess HM’s long term
memory
▪
▪ digit span + 1 test
▪ block-tapping memory-span test
▪
▪ HM had global amnesia - amnesia for
information presented in all sensory
modalities
▪ mirror drawing test
▪ incomplete pictures test
▪ pavlovian conditioning
▪ three major scientific contributions of HM’s case
▪
▪ by showing that the medial temporal lobes play an
especially important role in memory, H.M.’s case
challenged the then-prevalent view that memory
functions are diffusely and equivalently distributed
throughout the brain. In so do- ing, H.M.’s case
renewed efforts to relate individual brain structures
to specific mnemonic (memory-related) processes
▪ the discovery that bilateral medial temporal
lobectomy abolished H.M.’s ability to form certain
kinds of long-term memories without disrupting his
performance on tests of short-term memory or his
remote memory (memory for experiences in the
distant past) supported the theory that there are
different modes of storage for short- term, long-
term, and remote memory. H.M.’s specific prob- lem
appeared to be a difficulty in memory consolidation
(the translation of short-term memories into long-
term memories)
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▪ H.M.’s case was the first to reveal that an amnesic
patient might claim no recollection of a previous
experience while demonstrating memory for it by
improved performance (e.g., on the mirror-drawing
and incomplete-pictures tests).
▪
▪ This discovery led to the creation of two
distinct categories of long-term memories:
Conscious long-term memories became
known as explicit memories (or declarative
memories), and long- term memories
demonstrated by improved test performance
without conscious awareness became known
as implicit memories.
• retrograde amnesia - backward acting
• aneterograde amnesia - forward acting
• medial temporal lobe amnesia
•
o inability to form new long term memories
o tests that assess implicit memory are called repetition priming
tests
• semantic and episodic memories
•
o explicit long term memories
o semantic memories
o
▪ are explicit memories for general facts or information
o episodic memories
o
▪ explicit memories for the particular events of one’s life
o people with medial temporal lobe amnesia have particular difficult
with episodic memories
• effects of global cerebral ischemia on the hippocampus and memory
•
o global cerebral ischemia - an interruption of blood supply to the
entire brain - often suffer from medial temporal lobe amnesia
o selective damage can cause medial temporal lobe amnesia
o transient global amnesia
o
▪ defined by its sudden onset in the absence of any obvious
cause in otherwise normal adults
▪ case of medial temporal lobe amnesia
▪ severe anterograde amnesia and moderate retrograde
amnesia for explicit episodic memories - as seen in other
cases of medial temporal lobe amnesia
▪ in transient global amnesia - the amnesia is tangent -
typically lasting only 4 to 6 hours
▪ no brain pathology linked to the disorder
• amnesia of korsakoff’s syndrome
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•
o korsakoff’s syndrome
o
▪ a disorder of memory common in people who have
consumed large amounts of alcohol
o brain damage is associated with thiamine deficiency that often
accompanies heavy alcohol consumption
o post mortem examination typically reveals lesions to the medial
diencephalon - the medial thalamus and the medial hypothalamus
and diffuse damage to several other brain structures - the
neocortex, the hippocampus, and cerebellum
o during early stages of the disorder - anterograde amnesia for
explicit episodic memories is the most prominent symptom
o as the disorder progresses - retrograde amnesia also develops
o damage to mediodorsal nuclei of the thalamus
• amnesia of alzheimer’s disease
•
o first sign of the disease is often a mild deterioration of memory
o progressive disorder - eventually develops and becomes so severe
that the patient is incapable of simple activities e.g. eating,
speaking
o memory deficits are more general than those previously discussed
o major anterograde and retrograde deficits on tests of explicit
memory
o level of acetylcholine is reduced in the brains of alzheimer’s
patient
o
▪ this reduction results from the degeneration of the basal
forebrain - brains main source of acetylcholine - cause of
alzheimer’s amnesia
▪ not the only factor - medial temporal lobes and prefrontal
cortex are also involved
• amnesia after concussion - evidence for consolidation
•
o postraumatic amnesia
o
▪ amnesia following a nonpenetrative blow to the head
▪ testing usually reveals the patient has permanent
retrograde amnesia for the events that led up to the blow
and permanent anterograde amnesia for many of the events
that occurred during the subsequent period of confusion
▪ islands of memory - surviving memories for isolated events
that occurred during periods for which other memories
have been wiped out
o gradients of retrograde amnesia and memory consolidation
o
▪ gradients of retrograde amnesia after concussion seem to
provide evidence for memory consolidation
▪ hebb’s theory of memory consolation
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